1. Field of the Invention
The present invention relates to a finder optical system in a camera, and more particularly to a finder optical system in which an eyepiece is constituted with a single lens element.
2. Description of the Prior Art
In general, finder magnification of a finder optical system is defined as fo/fe, wherein fo represents a focal length of an objective lens and fe represents a focal length of an eyepiece. Accordingly, in order to increase the finder magnification, the focal length of of the objective lens has to be made larger or the focal length fe of the eyepiece has to be made smaller. In a lens shutter camera, the objective lens in the finder optical system and a photo-taking lens are separated from each other, and therefore if the focal length fo of the objective lens is lengthened, the total length of the finder optical system is also lengthened, which makes it difficult to attain the compactness of the whole finder optical system. Thus, the finder magnification of the lens shutter camera is generally small compared with that of a single lens reflex camera, and therefore an image in the finder becomes difficult to be seen clearly. For this reason, in various conventional lens shutter cameras, the finder magnification is intended to be made as large as possible by shortening the focal length fe of the eyepiece.
Further, it is usual that the eyepiece of the lens shutter camera consists of the combination of a negative lens element and a positive lens element, whereby achromatization is performed so as to correct chromatic aberration.
In view of the space, position accuracy, surface accuracy and cost, it is more advantageous to constitute the eyepiece with a single lens element. However, since achromatization is not performed, axial chromatic aberration becomes difficult to be corrected effectively by such simple constitution of the eyepiece. Particularly, as the focal length fe of the eyepiece is made smaller, the axial chromatic aberration turns for worse extremely.